The bonnets of ram type blowout preventers are generally secured to the preventer body with fasteners such as bolts or studs and nuts. To facilitate ram changes, the number of fasteners used has been minimized. With increased working pressures both fastener diameter and length increase to accommodate the increased pressure and the resultant increased bonnet thickness. The use of torque to tension bonnet bolting is not reliable since the torque-stress relationship for such fasteners varies substantially and with larger fasteners the torques recommended exceed the capacity of commonly available wrenching equipment.
Bolt tensioning equipment is available for use on pressure vessels, on large anchor bolts and other applications but such equipment is not well adapted for tensioning blowout preventer bonnet studs.
The J. L. Biach U.S. Pat. No. 3,015,975 and the R. E. Latham U.S. Pat. No. 4,075,923 each disclose a stud tensioning apparatus using a pressure responsive member to place the stud under tension. Biach provides a bevel gearing system to set the nut once the stud is under tension. The Latham device remains a part of the nut support permanently. The Biach apparatus tensions only one stud at a time and requires special gearing to set the nut since it is completely covered by the apparatus. A similar structure is available commercially but it differs by providing a port for access to the nut. The apparatus disclosed in the H. G. Darrington U.S. Pat. No. 4,015,801 is similar to such commercial device. Each of these devices tensions a single stud at a time. Multiple tensioning is accomplished only by multiple devices having a common pressure fluid manifold.
Such devices would not provide uniform tensioning of bonnet studs in minimum time and would not be a portable apparatus which can be used quickly and effectively on blowout preventers in the field.